This invention relates to paper handling systems, and more particularly, to a duplex copying apparatus which employs a multifeed detection device in a document handling system for pre-collation copying.
Bottom sheet feed devices have been employed as document handling means in the past and have included pressurized air to reduce friction between the bottom sheet and the sheet stack tray and minimize friction between the bottom sheet and sheets immediately adjacent thereto. In order to prevent misfeeds or multifeeds, a tri-roller feed belt has been employed having two stationary rolls and a movable roll, the stationary roll disposed beneath the edge of the sheet stack serving to support the feed belt against the lower sheet for feeding the sheet from the stack, the movable roller being disposed adjacent the aforesaid stationary roller for movement into engagement with the bottom sheet of the stack in the event that a sheet is not forwarded at the proper time under the influence of the belt section above the stationary roller. The displacement of the movable roller increases the surface area of the belt in contact with the bottom sheet of the stack to exert a greater feed force thereon.
Problems encountered during the use of such systems included some misfeeding and multifeeding of sheets which reduced reliability of the systems.
Multifeeds are important to control in document feeders since they directly affect output set integrity if undetected. Multifeeds are significantly more important in automatic document handlers as disclosed herein since they could result in jams, or worse, document damage if undetected.
The present invention is intended to overcome the above-mentioned disadvantages of unreliability in document feeders and comprises a drag roll system which is in contact and driven by the feed belt against an applied torque in the drag roll in the feed mode. The drag roll is synchronized with a motor that drives the feed belt. If a single document enters the nip between the drag roll and feed belt, or if no document is present in the nip, the drag roller will maintain a velocity synchronism with the motor. However, double documents or multi-documents entering the nip will cause the drag roller to hesitate with this resultant change in velocity being detected by a suitable sensor which transmits a shut-down signal, as well as a multi-feed indication to the copier console.